Hatz Biplane Association

Maybe I am a klutz at searching the forum - I am trying to understand why one soaks or steams cap strips, bows strips, etc. if it is important to have aircraft wood at a low level of moisture? I understand that wetting the wood helps with curves (from stick modeling days), but I do not want to destroy the wood's properties by increasing the cell water content. I recall that ammonia is used in modeling, but that too might weaken the wood's natural properties?

I found it only necessary to steam the portion of the capstrips associated with the leading edge of the ribs. You will steam them, then place them in a jig that establishes the curve and then let that dry for a day or two. Buy the time you use it in construction of your ribs, it should be dry again. No worries with loss of any strength.

Terrific news Jeff, thanks. Coincidentally I was just soaking balsa this week for bows on a Dumas R/C model of a Cessna Bird Dog. The Hatz looks a lot like model planes I have built, and also somewhat like a Stits Skycoupe I helped restore a few years back.

I did all my ribs and bows without steaming. I did some research. It's not the steam, it's the heat. Back in the day, they used the heat from the stove pipe to bend wood for violins. Once the wood cooled it stayed in place. Also wood will bend without breaking to a certain degree. Hard wood will bend more than softwood. There is a general formula I found on the Internet. Any of the bending for the ribs or bow are well withing the limits of how much wood will bend without breaking.

I also looked into how they did glue laminated beams and curved stair railing. Glue laminated beams have a slight cant in them so when weight is applied they straighten. Both are made up of several strips of wood glued together. Neither process pre bends the wood. They just use a jig and glue. Once the glue dries the bend is permanent.

In the end I decided that I didn't need to steam either my capstrips or the bow. See my blog below.

Making Ribs
Making the Wing Bow

Gorgeous work and very helpful tips Murray. Thank you again! Kent